A variety of devices for handling fluid streams, such as separators, compressors, and pumps, are known. Generally, a separator functions to separate a fluid stream into different phases, such as into liquid and gaseous portions, and/or may be used to remove solid matter from a fluid stream. Compressors and pumps basically function to compress or pressurize gases and pressurize liquids, respectively, often for the purpose of transporting the fluid, for example, within a pipeline. Typically, when a fluid stream is composed of both gaseous and liquid portions, the fluid stream must first be separated, and then the gaseous portions may be directed into a compressor, while the liquid portions may be directed into a pump so as to be separately treated. Such pumps generally include a rotary impeller powered by a driver or motor, and operate such that the fluid is accelerated by passing through the rotating impeller and then decelerated to increase the fluid pressure.
The separator and the compressor may be installed in a single casing, thereby providing an efficient, compact solution of compression system design. Such a system may be referred to as an integrated separator-compressor system. For the integrated separator-compressor system to be considered economical and commercially viable for use in onshore, offshore, and/or sub-sea applications, it is desirable that the number of stages of compression within the single casing be increased to increase the overall compressor pressure ratio within the single casing. However, current integrated separator-compressor systems face certain difficulties in satisfying this challenge. For example, increasing the number of stages of compression would increase the overall number of impellers required to achieve the desired compressor throughput (mass flow) and pressure rise. This would result in an increase in the length of the shaft and/or an increase in the distance between shaft bearings. An increased shaft length and bearing span would require an increased control of rotordynamics.
What is needed, therefore, is a compression system that provides an increased compression pressure ratio in a single casing in an economical and commercially viable manner.